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a*  a « 


JUN  1  6  2005 

MNliVERSlTYOFtLUNOjS, 


Agricultural  Experiment  Station, 


BULLETIN  NO.  91. 


PREVENTING  CONTAMINATION  OF  MILK. 


BY  WILDER  J.  FRASER. 


URBANA,  ILLINOIS,  DECEMBER,  1903. 


SUMMARY  OF  BULLETIN  No.  91. 

INTRODUCTION. — Investigation  has  shown  that  all  of  the  troublesome  changes 
that  take  place  in  milk  and  make  it  such  a  difficult  product  to  handle  properly  are 
caused  by  bacteria.  Page  221. 

BACTERIA. — Bacteria  are  single-celled  plants,  so  minute  that  several  hundred  of 
them  placed  closely  side  by  side  would  equal  only  the  thickness  of  ordinary  writing 
paper.  Page  221. 

SOURCES  OF  BACTERIA  IN  MILK. — Bacteria  exist  in  immense  numbers  in  the 
air,  and  in  dust  and  dirt  of  every  description,  and  for  this  reason  it  is  difficult  indeed 
to  secure  milk  free  from  germs.  Page  222. 

THE  EFFECT  OF  BACTERIA  ON  MILK. — Bacteria  not  only  cause  milk  to  sour  in 
a  short  time,  but  they  make  it  less  wholesome,  and  often  impart  a  bad  flavor. 

Page  223. 

OBJECT  OF  THE  INVESTIGATION. — The  purpose  of  the  investigation  reported  in 
this  Bulletin  was  to  determine  the  effect  of  the  different  common  operations  per- 
formed each  day  in  dairies  and  dairy  barns  upon  the  bacterial  content  of  milk,  and 
to  find  the  most  practical  methods  by  which  this  contamination  could  be  reduced 
to  the  least  possible  amount.  Page  224. 

METHOD  USED. — Petri  dishes  filled  with  a  sterile  nutrient  medium  were  exposed 
for  a  definite  length  of  time,  and  then  held  at  a  warm  temperature  for  three  days, 
when  the  colonies  were  counted.  The  basis  taken  was  the  number  of  colonies 
developed  on  63  square  centimeters  of  surface  from  a  half-minute  exposure. 

Page  224. 

CHECKS  ON  THE  WORK. — To  learn  whether  petri  dishes  might  become  con- 
taminated before  or  after  direct  exposure,  dishes  were  left  in  dusty  places  in  the 
barn,  but  not  exposed.  In  the  thirty-nine  dishes  thus  treated,  but  seven  colonies 
developed.  Page  227. 

BACTERIAL  CONDITION  OF  OUTDOOR  AIR. — Of  the  exposures  made  in  the  open 
field,  fifty  percent  were  sterile,  while  of  those  made  in  the  barnyard,  twelve  percent 
were  sterile.  Page  228. 

BACTERIAL  CONDITION  OF  AIR  IN  DAIRY  BARNS. — The  results  obtained  in 
these  barns  show  that  with  a  dry  and  dusty  floor  the  bacterial  content  of  the  air  is 
large  when  the  cows  are  in  the  barn,  even  though  they  are  not  brushed  and  no  hay 
or  bedding  is  moved.  With  an  efficient  system  of  ventilation  and  a  clean  cement 
floor,  the  number  of  bacteria  in  the  air  is  decreased  greatly.  Dust  arising  from 
brushing  cows  is  more  heavily  laden  with  bacteria  than  dust  from  most  other 
sources.  Page  229. 

EXPERIMENTAL  MILKING  ROOM. — The  dust  which  arises  from  brushing  cows, 
although  heavily  laden  with  bacteria,  soon  settles  when  the  room  remains  closed, 
and  in  half  an  hour  the  air  is  practically  free  from  bacteria.  Page  235. 

BOTTLING  ROOM. — Everything  in  this  room  is  kept  clean,  and  the  floor  is 
usually  damp.  Eighty  percent  of  the  exposures  made  there  were  sterile.  Page  236. 

WASHING  UDDERS  BEFORE  MILKING. — The  number  of  colonies  developed  from 
exposures  under  apparently  clean  unwashed  udders  was  three  times  as  many  as 
under  the  same  udders  after  washing.  With  soiled  or  muddy  udders,  such  as  are 
frequently  found  in  dairies,  the  benefits  derived  from  washing  udders  are  much 
greater  than  these  results  show.  Page  237. 

WEIGHT  OF  DIRT  WHICH  FALLS  INTO  MILK  DURING  MILKING. — With  udders 
that  were  apparently  clean  it  was  found  that  an  average  of  3£  times  as  much  dirt  fell 
from  the  unwashed  udders  as  from  the  same  udders  after  they  were  washed.  With 
soiled  udders  the  average  was  18,  and  with  muddy  udders  90  times  as  much  dirt 
from  the  unwashed  as  from  the  washed.  Page  243. 

CONCLUSIONS. — The  results  of  the  work  described  in  this  Bulletin  are  of  vital 
importance  to  the  practical  dairyman,  as  they  show  that  extreme  cleanliness  is 
absolutely  essential  to  the  most  successful  dairying.  Page  245. 


PREVENTING  CONTAMINATION  OF  MILK. 

BY  WILBER  J.  FRASER,  CHIEF  IN  DAIRY  HUSBANDRY. 

INTRODUCTION. 

It  has  long  been  known  that  extreme  cleanliness  is  absolutely  essen- 
tial to  the  most  successful  dairying,  but  the  real  reason  for  this  was  not 
known  until  within  the  last  few  decades.  Investigations  of  recent  years 
have  shown  that  all  of  the  troublesome  changes  that  take  place  in  milk 
and  make  it  such  a  difficult  product  to  handle  properly  are  caused  by 
bacteria.  In  fact,  successful  dairying  depends  largely  upon  the  ability 
to  limit  the  number  of  bacteria  obtaining  access  to  milk,  and  to  control 
those  that  cannot  be  kept  out. 

Milk  becomes  contaminated  in  so  many  ways  in  the  process  of  milking 
that  it  is  extremely  difficult  to  secure  it  free  from  germs,  but  this  has 
been  done  in  an  experimental  way  a  sufficient  number  of  times  to  prove 
that  milk  as  formed  in  the  milk  glands  of  a  healthy  cow  is  germ  free. 
Since  bacteria  invade  the  udder  to  some  extent,  and  develop  there,  milk 
as  drawn  from  the  udder  is  not  entirely  free  from  germs ;  this  is  especially 
true  of  the  first  milk  drawn. 

When  milk  is  secured  free  from  germs,  the  common  phenomenon  of 
souring  does  not  take  place,  but  it  remains  sweet  and  practically 
unchanged  indefinitely.  It  is,  therefore,  of  the  utmost  importance  not 
only  to  the  milk  producer  and  the  consumer,  but  to  the  butter  and 
cheese  maker  as  well,  that  this  ideal  condition  be  as  nearly  reached  as 
possible.  By  observing  a  few  precautions  dairymen  can  prevent  the 
contamination  of  milk  to  a  large  extent,  and  thus  produce,  at  but  slight 
trouble  or  expense,  a  much  better  and  more  valuable  as  well  as  a  longer 
keeping  product. 

BACTERIA. 

Comparatively  little  was  known  of  bacteria  until  within  the  last  two 
decades,  but  during  this  time  much  attention  has  been  given  to  the  study 
of  these  microscopic  plants,  and  the  knowledge  of  them  has  made  won-, 
derful  progress.  The  study  had  not  advanced  far  when  it  was  discovered 
that  certain  species  of  bacteria  had  the  power  to  produce  disease,  and  the 
reputation  which  they  thus  gained  clings  to  all  bacteria  in  the  popular 
mind  to-day.  With  many  people  the  words  "bacteria"  and  "disease" 
are  nearly  synonymous  terms,  although  the  power  to  produce  disease 
belongs  to  a  small  percentage  only  of  the  numerous  species  of  these 
organisms.  Bacteria  are  the  chief  agents  in  decay,  and  without  decay 
all  organic  matter  would  remain  unchanged  after  death. 

221 


222  BULLETIN  No.  91.  [December, 


SIZE. 

These  organisms,  which  are  of  such  great  importance,  are  so  extremely 
minute  that  it  is  difficult  to  gain  an  adequate  conception  of  their  size. 
If  they  could  be  placed  closely  side  by  side,  it  would  take  several  hundred 
to  equal  the  thickness  of  ordinary  writing  paper.  Of  course,  they  can 
be  seen  only  with  the  most  powerful  microscope.  If  bacteria  could  be 
magnified  to  the  size  of  base-balls,  a  man  enlarged  in  the  same  propor- 
tion'would  be  over  fifty  miles  high. 

FORM. 

In  the  more  complex  species  of  plants  and  animals,  each  has  a  form 
peculiar  to  itself.  In  bacteria,  which  are  single-celled  plants,  there  can 
be  little  difference  in  the  form  of  the  different  species  because  of  their 
simple  structure  and  minute  size.  Although  there  are  hundreds  of 
species  of  bacteria,  they  all  come  under  three  different  forms,  which  may 
be  represented  by  balls,  rods,  and  corkscrews. 

[  SOURCES  OF  BACTERIA  IN  MILK. 

Since  milk,  as  formed  in  the  milk  glands  of  a  healthy  cow,  is  germ 
free,  we  would  not  expect  to  find  bacteria  always  present  in  it,  at  least  in 
such  large  numbers  as  usually  exist.  Freshly  drawn  milk  may  contain 
from  200  to  100,000  bacteria  per  c.  c.,  or  from  800  to  400,000  per  tea- 
spoonful,  according  to  the  care  with  which  it  is  handled.  By  the  time 
milking  is  completed,  under  ordinary  conditions,  the  milk  is  badly  con- 
taminated indeed.  It  is  then  of  the  greatest  importance  to  the  dairy 
interests  to  learn  the  sources  of  bacteria  which  gain  access  to  milk. 
The  number  found  in  freshly  drawn  milk  is  a  good  indication  of  the 
sanitary  conditions  under  which  it  was  produced. 

Let  us  pause  for  a  moment  and  see  where  these  bacteria  are  in  nature, 
and  how  they  so  readily  gain  access  to  milk.  Investigation  has  shown 
that  their  presence  is  well-nigh  universal.  They  are  found  floating  on 
the  dust  in  the  air,  and  in  the  soil  and  water.  It  is  difficult  to  find  a 
cubic  yard  of  air  that  does  not  contain  thousands  of  them,  and  soil  and 
water  contain  them  in  vastly  larger  numbers.  In  the  air  of  enclosed 
spaces,  as  in  dwellings  and  barns,  they  are  much  more  numerous  than 
out  of  doors.  In  the  air  of  barns  they  are  generally  abundant,  especially 
if  a  dust  has  been  raised.  They  are  also  found  in  immense  numbers  in 
dung  and  dirt  of  every  description,  on  the  cows'  udders,  the  hands  of  the 
milkers,  and  not  jonly  in  the  seams  and  cracks  of  unsterilized  dairy 
utensils,  but  also  clinging  to  the  entire  surface.  Wherever  there  is  a 
lodging  place  for  dust,  there  bacteria  will  be  found  in  vast  numbers. 
The  least  stir  in  the  bedding  or  of  the  dust  on  the  floor  will  send  myriads 
of  them  floating  into  the  air.  Everywhere  in  nature,  then,  these  organ- 


1903.]  PREVENTING  CONTAMINATION  OF  MILK.  223 

isms  exist  with  the  power  to  multiply  with  astonishing  rapidity  unless 
held  in  check  by  the  conditions  surrounding  them.  In  most  places  they 
are  dormant  or  growing  very  slowly.  The  bacteria  clinging  to  the  hair 
and  dirt  on  a  cow  and  those  riding  on  the  dust  in  the  air,  multiply  slowly, 
if  at  all,  but  they  have  the  power  of  growth,  and  as  soon  as  they  find 
moisture  and  nourishment,  they  develop  rapidly  if  the  temperature  is 
favorable. 

Freshly  drawn  milk  is  especially  adapted  to  the  growth  of  nearly  all 
species  of  bacteria,  as  it  contains  all  the  elements  necessary  for  their 
development,  and  besides  affords  a  favorable  temperature.  Those  that 
gain  access  to  it,  therefore  not  only  contaminate  it  themselves,  but 
multiply  at  an  astonishing  rate  if  the  milk  is  not  immediately  cooled  to 
near  the  freezing-point.  The  increase  of  bacteria  usually  occurs  by  the 
simple  division  of  one  individual  into  two.  The  exceptional  power  of 
rapid  multiplication  is  one  of  their  most  important  properties,  especially 
in  relation  to  dairying.  In  some  species  one  germ  may  become  two, 
under  favorable  conditions,  in  half  an  hour.  Such  multiplication  in  a 
geometrical  ratio  results  in  an  increase  of  numbers  with  almost  incon- 
ceivable rapidity.  At  this  rate,  starting  with  1  organism,  in  half  an 
hour  there  would  be  2;  in  one  hour  each  of  these  would  have  again 
divided,  making  4;  in  one  and  a  half  hours  8,  in  two  hours  16,  in  three 
hours  64,  in  four  hours  256,  etc.,  and  if  this  rate  of  multiplication  could 
be  maintained  for  twenty-four  hours  there  would  be  some  17,000,000, 
all  the  offspring  of  a  single  bacterium  within  a  single  day.  Fortunately 
for  humanity  this  maximum  multiplication  rarely  occurs,  as  various 
factors  soon  interpose  to  check  the  development  of  these  germs. 

Temperature,  moisture,  and  food  supply  are  the  conditions  controlling 
the  multiplication  of  bacteria.  Milk  at  all  temperatures  furnishes  ideal 
conditions  as  to  moisture  and  food,  and  when  freshly  drawn  its  tem- 
perature is  ideal  for  most  species.  This  being  the  case,  all  germs  that 
gain  access  to  milk  may  multiply  rapidly  unless  checked  by  an  arti- 
ficially low  temperature  or  by  the  addition  of  some  substance  that  pre- 
vents growth. 

The  temperature  at  which  bacteria  multiply  most  rapidly  varies  with 
the  species.  Some  grow  best  at  75°  F.,  and  others  at  90°,  while  a  few 
reach  their  maximum  rate  of  development  at  still  higher  temperatures. 

THE  EFFECT  OF  BACTERIA  ON  MILK. 

The  cow  is  a  much  more  economical  producer  of  human  food  than  is 
the  steer  or  the  pig,  and  if  bacteria  could  be  prevented  from  getting  into 
milk,  dairying  would  be  a  far  more  remunerative  occupation  than  it 
now  is. 

In  milk,  for  whatever  purpose  it  is  to  be  used,  nearly  all  species  of 
bacteria  are  detrimental.  They  not  only  cause  it  to  sour  in  a  short  time. 


224  BULLETIN  No.  91.  [December, 

but  make  it  less  wholesome  for  infants  and  invalids,  as  well  as  often 
impart  a  bad  flavor.  Certain  species,  however,  are  essential  in  the  manu- 
facture of  good  butter  and  cheese. 

The  changes  which  bacteria  produce  in  milk  are  several;  the  most 
common,  and  also  the  most  important  one,  being  the  conversion  of  milk 
sugar  into  lactic  acid,  which  is  known  as  souring.  Owing  to  the  rapid 
changes  which  bacteria  cause  in  milk,  it  is  not,  as  ordinarily  handled,  in 
suitable  condition  for  human  food  for  longer  than  twelve  to  forty-eight 
hours  after  it  is  drawn,  the  time  depending  upon  the  temperature  at 
which  it  is  held.  It  is,  then,  essential  that  every  family  receive  daily  a 
fresh  supply  of  milk.  This  necessitates  the  expenditure  of  a  large 
amount  of  time  and  labor  in  delivering  the  milk.  Generally  speaking, 
it  costs  as  much  to  deliver  milk  'to  the  consumer  after  it  is  produced  as  it 
does  to  produce  it.  From  this  it  is  seen  that  were  it  not  for  the  action 
of  bacteria,  a  large  supply  of  milk  could  be  delivered  at  one  time,  and 
thus  reduce  the  delivery  to  once  a  week,  or  even  less  frequently,  which 
would  increase  the  producer's  profit  several  fold  or  greatly  reduce  the 
price  to  the  consumer. 

When  we  consider  that  milk  is  used  daily  by  all  classes  of  people,  it 
will  be  seen  that  the  action  of  bacteria  on  milk  is  of  the  utmost  import- 
ance from  a  financial  standpoint  alone.  In  connection  with  this,  the 
health  of  the  community  should  be  considered,  for  disease  germs  fre- 
quently find  their  way  into  milk  where  slovenly  methods  are  practiced, 
and  thus  endanger  not  only  the  health  but  even  the  lives  of  the  con- 
sumers. 

OBJECT  OF  THE  INVESTIGATION. 

The  purpose  of  the  investigation  reported  in  this  bulletin  was  to 
determine  the  effect  of  the  different  common  operations  performed  each 
day  in  dairies  and  dairy  barns  upon  the  bacterial  content  of  milk,  and  to 
find  the  most  practical  methods  by  which  this  contamination  could  be 
reduced  to  the  least  possible  amount. 

METHOD  USED. 

In  this  investigation  nearly  all  of  the  results  were  obtained  by  expos- 
ing petri  dishes,  which  are  circular  glass  dishes  with  vertical  sides  having 
covers  similar  in  shape  only  large  enough  to  fit  easily  over  the  sides,  as 
shown  in  cut  No.  1.  The  dishes  used  for  this  work  were  one-half  inch 
deep  and  three  and  a  half  inches  in  diameter,  the  bottom  containing 
sixty-three  square  centimeters  of  surface.  These  dishes  were  washed, 
and  sterilized  by  baking  in  an  oven  at  a  temperature  of  140°  C.  or  284°  F. 
for  twenty  minutes.  Enough  sterilized  beef  broth  containing  three- 
fourths  of  one  percent  agar  was  then  poured  into  them  to  cover  the 
bottoms  of  the  dishes  about  one-eighth  inch  deep.  The  beef  broth 
furnished  the  nutrient  material  for  the  growth  of  the  bacteria,  and  the 


1903.] 


PREVENTING  CONTAMINATION  OF  MILK. 


225 


agar  caused  it  to  solidify  when  cool,  so  that  it  would  not  run  when  the 
dishes  were  tilted.  These  sterilized  dishes  were  filled  with  the  sterile 
nutrient  medium  in  a  laboratory  where  the  air  was  comparatively  free 
from  bacteria,  so  that  the  least  possible  contamination  would  take  place 
during  filling.  The  dishes  were  then  held  at  a  warm  temperature  for 
two  days,  so  that  if  any  were  contaminated  they  could  be  easily  detected, 
for  in  that  time  the  bacteria  would  have  developed  into  colonies  large 
enough  to  be  visible,  and,  of  course,  all  dishes  not  sterile  were  rejected. 


CUT  1. — PETRI  DISHES  FILLED  WITH  NUTRIENT  MEDIUM,  READY  TO  BE  EXPOSED. 

These  sterile  dishes  were  kept  closed  and  carried  to  the  place  of 
exposure  in  a  carrying  case  made  for  the  purpose.  An  exposure  was 
made,  as  shown  in  cuts  2  and  3,  by  placing  a  petri  dish  in  a  horizontal 
position,  removing  the  cover  for  a  definite  length  of  time,  then  quickly 
replacing  it.  After  being  exposed,  the  dishes  were  returned  to  the  labo- 
ratory, where  they  were  held  at  a  warm  temperature  for  three  days. 
Wherever  a  colony  developed  it  showed  that  the  dish  had  become  con- 
taminated by  one  or  more  bacteria  falling  on  the  nutrient  medium  in  the 
dish  at  the  time  of  exposure,  and  by  counting  these  colonies  the 
number  of  places  that  bacteria  had  fallen  on  the  medium  was  determined. 

That  an  accurate  record  of  all  exposures  might  be  kept,  the  dishes 
were  numbered  consecutively  as  exposed,  and  the  date,  place,  condition 
of  exposure,  and  length  of  time  exposed  were  recorded. 

In  this  work  the  basis  taken  was  the  number  of  colonies  developed  on 
sixty-three  square  centimeters  of  surface  for  a  half-minute  exposure.  In 
some  places  the  exposures  were  necessarily  for  a  shorter  time,  or  the  colonies 


226 


BULLETIN  No.  91. 


[December, 


would  have  been  entirely  too  numerous  to  count.  For  example,  under 
udders  the  exposures  were  usually  for  only  five  seconds,  and  the  actual 
number  counted  in  each  case  was  multiplied  by  six  to  bring  it  to  the 
basis  of  an  exposure  of  thirty  seconds. 

In  this  investigation  1,185  petri  dishes  were  exposed.  As  the  tables 
giving  a  complete  record  of  these  exposures  are  too  extensive  for  publi- 
cation, and  of  little  general  interest,  they  were  condensed  by  dividing 
the  exposures  into  groups  as  far  as  possible  and  the  average  for  each 


CUT  2. — EXPOSING  PETRI  DISH  IN  HANDS  UNDER  UDDER  DURING  MILKING. 

group  is  given.     Averages  were  computed  only  when  several  exposures 
were  made  at  the  same  time  and  under  similar  conditions. 

The  first  column  of  each  table  contains  the  laboratory  number  of  the 
dish,  or  the  first  number  of  a  group  of  dishes  exposed  at  the  same  time 
and  place,  and  the  second  column  gives  the  date  of  exposure.  The  first 
column  at  the  right  gives  the  number  of  exposures  averaged,  and  the 
remaining  column  or  columns  the  actual  or  average  number  of  colonies 
developed. 


1903.]  PREVENTING  CONTAMINATION  OF  MILK.  227 

CHECKS  ON  THE  WORK. 

As  a  further  check  against  error  and  to  learn  whether  petri  dishes 
might  become  contaminated  before  or  after  direct  exposure,  certain  tests 
were  made. 

January  21,  four  dishes  were  carried  in  the  barn  for  five  minutes 
at  a  brisk  walk  without  removing  the  cover.  Only  one  developed  a 
colony,  and  that  but  a  single  one.  On  the  same  day  one  dish  stood  for 


CUT  3. — PETRI  DISH  CLOSED  JUST  AFTER  BEING  EXPOSED  UNDER  UDDER. 

twenty-five  minutes  in  the  barn  and  another  was  moved  rapidly  for  five 
minutes  through  the  dust  arising  from  a  pile  of  fodder  freely  agitated 
with  a  fork.  Both  covers  were  left  closed,  and  neither  developed  a 
colony. 

Again,  twenty-eight  dishes  stood  covered  for  five  days  in  the  dairy 
building,  and  twenty-three  or  eighty-two  percent  remained  sterile. 

March  10,  five  dishes  still  in  the  carrying  case  stood  for  one  hour 
in  the  barn.  These  same  dishes  had  been  standing  for  five  days  in  the 
dairy  building.  Only  one  dish  developed  a  single  colony.  From  all 
of  which  it  is  concluded  that  petri  dishes  are  not  subject  to  contam- 
ination even  when  in  motion  in  a  dusty  barn  except  while  the  cover  is 
removed. 


228  BULLETIN  No.  91.  [December, 

TABLE  1. — BACTERIAL  CONDITION  OF  OUTDOOR  AIR. 


Laboratory  num- 
ber of  group. 

Date  of  exposure. 

Place  and  condition  of  exposure. 

Exposures  aver- 
aged. 

Colonies 
developed. 

§13 

S3 

H 

(8.S, 

139 
176 
177 
227 
236 
237 
238 
255 
256 
257 
274 
276 
279 
281 
325 
326 
359 
398 
402 
406 

613 
634 
639 
895 
905 
917 

1897 
March  10 
April  24 

June  3 
u 

it 
u 

u 
July  2 
u 

Sept.  14 
u 
Oct.  28 

1899 
May  11 
May  14 

June  3 
Sept.  16 

30  rd.  from  any  building    

4 
2 
2 
1 
1 
1 
2 
1 
1 
1 
2 
3 
2 
1 
1 
1 
2 
4 
4 
1 

14 
10 
12 
10 
8 
3 

t 

0 
0 

2" 

& 
"i 

'3f 

4 
0 
80 
3 
18 

4 
21 
IS 
5 
1 
1 
1 
12 
17 
86 
46 

2J 

Ii9o 

'ej 

On  post  6  rd.  from  barn,  just  after  shower  .  .  . 
Same  as  No.  176,  only  at  foot  of  post  

3  ft.  from  ground  

3  ft.  from  damp  ground,  no  breeze  

Same  as  No.  236,  only  on  ground,  slight  breeze 
Same  as  No.  237,  only  air  quiet  

On  post  6  ft.  from  barn,  wind  from  barn    .... 

On  post,  wind  blowing  across  pasture  .           .  . 

3  ft.  from  ground,  1  rod  east  of  barn  

On  ground,  1  rod  east  of  barn  

Same  as  No.  274,  only  on  post  

On  ground  

Same  as  No.  279,  only  on  post  

On  post,  1  rod  east  of  barn  

Same  as  No.  325,  only  on  ground  

On  post  in  dusty  yard,  wind  from  cows  

In  dusty  yard,  wind  from  grassy  field  

In  dusty  yard  among  cows,  no  breeze 

In  dusty  yard  after  cows  were  let  out  

Gentle  breeze,  shower  night  previous             .  .  . 

On  ground  in  barnyard  

On  ground  in  grassy  pasture.! 

On  ground  in  barnyard  

On  ground  in  grassy  pasture  

On  ground  in  barnyard  .... 

Averaee  . 

0.9 

IB 

Table  1  shows  the  average  number  of  colonies  that  developed  in 
petri  dishes  from  exposures  made  at  different  times  in  the  open  field  and 
in  the  barnyard. 

By  referring  to  the  column  containing  the  results  of  exposures  made 
in  the  open  field,  it  is  seen  that  the  group  averages  range  from  0  to  3f 
colonies,  and  that  the  average  of  the  entire  forty-three  exposures  was 
less  than  one  colony.  From  the  last  column,  which  shows  the  results  of 
exposures  made  in  the  barnyard,  it  is  seen  that  the  group  averages  range 
from  0  to  86  colonies,  with  an  average  for  the  fifty-one  exposures  of  13 
colonies.  Of  the  exposures  made  in  the  open  field,  fifty  percent  were 
sterile,  while  of  those  made  in  the  barnyard  only  twelve  percent  were 
sterile,  showing  that  the  air  in  the  open  field  was  comparatively  free 
from  bacteria,  while  that  in  the  barnyard,  where  the  ground  was  bare 
and  dusty,  contained  more. 


1903.] 


PREVENTING  CONTAMINATION  OF  MILK. 


229 


BACTERIAL  CONDITION  OF  AIR  IN  DAIRY  BARNS. 
The  two  following  tables  show  the  results  from  exposures  made  in 
dairy  barns  varying  in  their  sanitary  condition "  and  care.     They  also 
show  the  effect  upon  the  bacterial  content  of  the  air  of  the  different 
common  operations  performed  in  dairy  barns. 

TABLE  2. — DAIRY  BARN  No.  1. 

Frame  barn,  30x50  ft.,  containing  two  rows  of  cows;  tight  floor  overhead; 
plank  floor  under  cows;  dirt  floor  back  of  cows;  cobwebs  numerous. 


Place  and  condition  of  exposure. 


1.8 


1897 

232  June  15        Barn  vacant,  open,  air  still,  floor  dry 5 

233  Barn  vacant,  open,  air  still,  floor  dry 33 

234  Barn  vacant,  open,  air  still,  floor  dry 19 

235  Barn  vacant,  open,  air  still,  floor  dry 50 

Average  27 

After  cows  were  let  in 150 

After  cows  were  let  in 54 

After  cows  were  let  in 44 

After  cows  were  let  in 24 

Average  68 

245  After  No.  240,  in  window,  wind  blowing  out 44 

246  Same  as  No.  245,  only  another  window 208 

Average  126 

247  In  window,  opposite  side,  wind  blowing  in 4 

248  Same  as  No.  247,  only  another  window 44 

Average  24 

250  Back  of  cows,  3  ft.  from  floor,  30  min.  after  No.  240.  .       34 

252  Back  of  cows  on  floor,  30  min.  after  No.  240 36 

253  4  ft.  from  floor  between  two  rows  of  cows 150 

254  " On  floor 718 

DAIRY  BARN  No.  2.     H.  B.  GURLER. 

Barn  50x60  ft.,  containing  four  rows  of  cows;  cement  floor,  wooden  stalls, 
sides  and  ceiling  whitewashed.     Milking  in  progress. 

332        Oct.  20         Middle  of  west  end,  cows  eating  grain  and  silage  ....  2 

336  Northwest  corner 51 

337  Northeast  corner,  wind  blowing  in   16 

340  Northwest  corner 37 

341  Southeast  corner  29 

342  Middle  of  barn 23 

343  Middle  of  barn 86 

344  Middle  of  barn 18 

Middle  of  barn,  just  after  letting  out  cows 30 

346                             Middle  of  barn,  just  after  letting  out  cows 26 

Average 32 


230  BULLETIN  No.  91.  [December, 

In  Table  2  the  result  of  each  exposure  is  given,  and  the  average  of 
each  group  is  shown  in  heavy  type. 

June  15,  when  the  barn  had  been  vacant,  but  open  for  six  hours, 
and  the  air  was  comparatively  still  out  of  doors,  four  exposures  averaged 
27  colonies,  for  so  much  of  the  floor  was  dry  and  dusty  that  the  air  in  the 
barn  was  far  from  sterile.  After  the  cows  were  let  in,  four  exposures 
averaged  68  colonies,  indicating  that  letting  in  the  cows  had  increased 
the  bacterial  content  of  the  air  two  and  one-half  times.  Immediately 
following  these,  two  exposures  in  a  window,  wind  blowing  out,  averaged 
126  colonies,  which  is  nearly  twice  as  many  as  were  obtained  from  an 
average  of  four  exposures  made  at  different  places  in  the  barn  just  before. 
Two  exposures  in  a  window,  wind  coming  in,  averaged  24  colonies,  show- 
ing that  the  air  was  not  badly  infected  when  entering  the  barn,  but  that 
it  became  so  while  there. 

Exposures  Nos.  250  and  252,  made  back  of  the  cows,  showed  34  and 
36  colonies,  while  at  the  same  time  two  exposures  made  in  feed  alley 
between  rows  of  cows  showed  150  colonies  three  feet  from  the  floor,  and 
718  on  the  floor,  from  which  it  appears  that  there  were  many  more 
bacteria  in  the  center  than  at  the  sides  of  the  barn,  and  more  at  the  floor 
than  three  feet  above. 

From  the  results  obtained  in  this  barn  we  learn  that  with  a  dry  and 
dusty  floor  the  bacterial  content  of  the  air  is  high  when  the  cows  are  in 
the  barn,  even  though  they  are  not  brushed  and  no  hay  or  bedding  is 
moved. 

At  the  time  the  ten  exposures  were  made  in  dairy  barn  No.  2,  the  barn 
was  full  of  cows  eating  grain  and  silage  and  four  men  were  milking.  The 
number  of  colonies  that  developed  in  the  different  dishes  ranged  from 
2  to  86,  with  an  average  of  32.  This  difference  was  doubtless  due  to 
local  conditions,  as  a  cow  switching  her  tail  near  the  exposed  dish  might 
send  myriads  of  bacteria  into  the  air  at  that  place.  The  low  average 
shows  that  the  air  was  comparatively  free  from  bacteria  for  a  barn  full  of 
cows  and  when  milking  was  in  progress.  This  condition  was,  no  doubt, 
due  to  the  fact  that  the  barn  was  built  and  cared  for  in  a  most  sanitary 
manner.  An  excellent  system  of  ventilation  was  provided,  the  cement 
floor  was  scrubbed  clean  every  day,  sides  and  ceiling  were  whitewashed 
and  no  cobwebs  were  allowed  to  collect. 


1903.] 


PREVENTING  CONTAMINATION  OF  MILK. 


231 


TABLE  3. — BACTERIAL  CONDITION  OF  AIR  IN  DAIRY  BARN  No.  3. 

Stone  basement,  32x40  ft.,  containing  two  rows  of  cows;  tight  floor  above, 
paved  floor  below;  an  inch  of  dusty  chaff  on  floor;  cobwebs  numerous. 


Laboratory  num- 
ber of  group. 

Date  of 
exposure. 

Place  and  condition  of  exposure. 

Exposures 
averaged. 

Colonies 
developed. 

351 

1897 
Oct.  25 

Just  before  cows  were  let  in  ;  barn  vacant  all  day, 
except  8  calves  in  end  

6 

152 

363 

H 

Immediately  after  cows  were  let  in  

5 

202 

371 

a 

1  hr.  after  No.  363  

6 

192 

381 

" 

30  min.  after  No.  371,  just  after  letting  out  the 
cows                           

4 

150 

387 

Oct.  28 

Conditions  same  as  No.  351   

6 

126 

394 

u 

Window  sill,  slight  breeze  blowing  in  from  empty 
yard  

a 

30 

396 
408 

a 

u 

After  No.  394,  in  open  door,  wind  blowing  out  .  . 
Same  as  No.  394,  only  5  min.  later,  cows  having 
been  let  in  barn  in  meantime  

2 

?, 

75 
39 

410 

u 

Same  as  No.  408,  only  in  door  on  opposite  side, 
wind  blowing  out  

?, 

66 

412 

" 

30  min.  after  cows  were  let  in;  exposures  made  in 
different  parts  of  barn  

fi 

129 

422 
424 

u 
u 

30  min.  after  No.  410,  in  door  wind  blowing  out. 
30  min.  after  No.  408,  same  window,  brisk  breeze 
blowing  in  from  vacant  yard               

2 
? 

325 

77 

426 

u 

5  min.  after  No.  422,  in  door  wind  blowing  out, 
cows  let  out  in  meantime  

2 

321 

428 

" 

In  yard  below  window  where  No.  424  was  ex- 
posed   

1 

76 

DAIRY  BARN  No.  4,  UNIVERSITY  OF  ILLINOIS. 


73 

78 

Feb.  13 

u 

After  sweeping  and  feeding,  cows  eating  roughage 
1£  hr.  after  No.  73,  a  little  bedding  put  in  20  rain, 
previous                              

4 

o 

94 

72 

83 
90 

u 

Feb.  23 

20  min.  after  No.  78,  6  cows  brushed  in  meantime 

After  feeding  chopped  fodder  and  sweeping,  dust 
visible      .      

2 
6 

692 

84 

96 

u 

40  min.  after  No.  90;  barn  quiet  in  meantime,  ex- 
cept cows  eating             

6 

61 

104 

" 

25  min.  after  No.  96;  13  cows  brushed  in  mean- 
time .                                         

10 

159 

121 

March  10 

After  feeding  and  sweeping;  doors  open,  strong 
wind  from  south     

6 

40 

127 

H 

1  hr.  after  No.  121,  barn  open  in  meantime,  strong 
breeze  from  south  

6 

84 

133 

u 

20  min.  after  No.  127  ;  10  cows  brushed  in  mean- 
time, barn  open,  windy  

6 

44 

152 

158 

April  24 

» 

Cows  in,  eating  oat  hay  ;  barn  closed  and  swept  .  . 
1  hr.  after  No.  152;  barn  quiet  except  cows  eating 
hay                   

6 

4 

57 
119 

164 

u 

20  min.  after  No.  158;  11  cows  brushed  in  mean- 
time .                                       

5 

131 

170 

" 

10  min.  after  No.  164;  barn  quiet  in  meantime.  . 

1 

53 

232  BULLETIN  No.  91.  [December, 

TABLE  3. — BACTERIAL  CONDITION  OP  AIR  IN  DAIRY  BARN  No.  4 — Continued. 


Laboratory  num- 
ber of  group. 

Date  of 
exposure. 

Place  and  condition  of  exposure. 

Exposures 
averaged. 

Colonies 
developed. 

178 

1897 
May  4 

Cows  in,  eating  hay;  barn  closed  for  15  min  

6 

62 

184 

20  min.  after  No.  178;  8  cows  brushed  in  mean- 
time.. 

6 

92 

190 
206 

June  3 

15  min.  after  No.  184;  barn  quiet  in  meantime  .  . 

Barn  quiet,  cows  let  in,  all  quiet  15  min.;  small 
amount  of  bedding  in  stalls   

3 
q 

59 
46 

218 

a 

20  min.  after  No.  206;  11  cows  brushed  in  mean- 
time.. 

6 

88 

268 

July  2 

10  cows  in,  brushed,  quiet  15  min.,  windows  open 
on  one  side,  no  wind,  damp  outside  

6 

12 

285 

July  10 

Cows  in,  bedded,  and  fed  hay;  no  rain,  and  very 
hot  for  10  days  

? 

55 

316 

Sept.  14 

Milking  in  progress  

3 

276 

465 

1898 
Nov.  30 

Barn  empty,  swept,  and  closed  for  3  hours;  snow 
on  ground  3  days 

6 

i 

471 

K 

10  min.  after  No.  465  . 

fi 

| 

477 

" 

30  min.  after  No.  465;  cows  let  in,  fed  chopped 
fodder;  floor  swept,  dust  slightly  visible  

1 

236 

478 

a 

30  min.  after  No.  465;  cows  let  in,  fed  chopped 
fodder;  floor  swept,  dust  slightly  visible  

1 

291 

479 

u 

30  min.  after  No.  465;  cows  let  in,  fed  chopped 
fodder;  floor  swept,  dust  plainly  visible 

1 

412 

480 

V 

30  min.  after  No.  465;  cows  let  in,  fed  chopped 
fodder;  floor  swept,  no  dust  visible  

7 

151 

488 
498 

u 

1  hr.  after  No.  480;  cows  eating  in  meantime.  .  .  . 
10  min.  after  No.  488;  16  cows  brushed  in  mean- 
time    ...               ... 

9 
?, 

84 
858 

931 

1901 
June  5 

Milking  in  progress;  no  hay  moved  for  1  hr.  ;  barn 
open,  slight  breeze 

1? 

•7i 

282 

1897 
July  2 

On  floor,  south  door  of  barn,  slight  breeze  from 
south,  5  cows  in  barn  

1 

0 

283 

« 

On  floor,  center  of  barn,  no  breeze  

1 

29 

284 

u 

On  floor,  north  door  of  barn,  no  breeze 

1 

33 

3?? 

1897 
Sept.  14 

3  ft.  from  cow  being  brushed  

?, 

800 

497 

1898 
Nov.  30 

3  ft.  from  cow  being  brushed  

1 

600 

487 

u 

Feed  room  after  corn  meal  was  let  down  from  bin 
above,  much  dust  visible  

1 

20 

500 

Dec.  8 

Feed  room  after  corn  meal  was  let  down  from  bin 
above,  much  dust  visible  . 

4 

4* 

51? 

u 

10  min.  after  No.  500  . 

? 

6 

516 

u 

Behind  8  cows  just  after  being  brushed  4  min.; 
less  dust  visible  than  at  No.  500  

4 

764 

^99 

u 

5  min.  after  No.  51C  . 

? 

123 

524 

u 

10  min.  after  No.  516  .  . 

2 

150 

1903.]  PREVENTING  CONTAMINATION  OF  MILK.  233 

TABLE  3. — BACTERIAL  CONDITION  OF  AIR  IN  DAIRY  BARN  No.  4 — Continued. 


Laboratory  num- 
ber oi  group. 

Date  of 
exposure. 

Place  and  condition  of  exposure. 

Exposures 
averaged. 

Colonies 
developed. 

566 

1899 
April  13 

Behind  cows,  milking  in  progress.. 

2 

60 

59? 

May  11 

Behind  cows,  milking  in  progress  

4 

8t 

628 

May  14 

Feed  room  after  musty  corn  meal  was  let  down 
from  bin  above  

? 

284 

630 

u 

Barn  loft  3  min.  after  hay  was  moved,  small 
amount  of  dust  visible  

4 

7i 

700 

May  16 

On  floor  back  of  cows,  milking  in  progress  

8 

8i 

713 
717 

May  19 

Barn  loft  after  pitching  hay,  dust  plainly  visible  . 
Same  place  as  No.  713    3  min.  later. 

4 
4 

323 
45 

725 
721 

„ 

Immediately  after  No.  717,  on  beam  8  ft.  above. 
Same  place  as  No.  717,  3  min.  later  

2 
4 

27 
22 

727 

a 

In  feed  room  after  corn  meal  was  let  down  from 
bin  above,  dust  plainly  visible  

4 

57 

731 

it 

Same  place  as  No.  727,  3  min.  later  

4 

15 

735 

« 

Same  place  as  No.  731,  3  min.  later  

4 

12 

739 

« 

In  feed  room  after  bran  was  let  down  from  bin 
above,  dust  slightly  visible    

4 

418 

743 

a 

Same  place  as  No.  739,  3  min.  later  

3 

6 

830 

Mav  28 

On  floor  back  of  cows,  milking  in  progress  

2 

4 

83? 

In  front  of  cows,  milking  in  progress  

3 

11 

850 

June  3 

On  floor  back  of  cows,  milking  in  progress 

5 

31 

885 

After  bran  was  let  down  from  bin  above,  dust 
slightly  visible  

5 

114 

890 

« 

Same  place  as  No.  885,  6  min.  later 

5 

8f 

927 

Sept.  16 

On  floor  back  of  cows,  milking  in  progress.. 

4 

19 

October  25  and  28,  exposures  were  made  in  a  barn  that  had 
been  vacant  all  day  excepting  eight  calves  in  one  end.  From  the  num- 
ber of  colonies  which  developed  it  is  seen  that  when  the  barn  floor  is 
dry  and  dusty,  and  cobwebs  are  allowed  to  collect,  the  bacterial  con- 
tent of  the  air  is  high  if  there  are  animals  moving  about.  In  such 
jases  the  number  of  bacteria  is  increased  but  slightly  by  letting  in  the 
cows. 

These  results  show  that  under  normal  conditions  air  which  enters 
windows  and  doors  is  comparatively  sterile,  while  that  which  passes  out 
is  badly  contaminated. 

Barn  No.  4  in  Table  3  was  the  University  dairy  barn  before 
being  remodeled. 


234  BULLETIN  No.  91.  [December, 

The  floor  of  the  barn  was  swept  each  day  and  no  cobwebs  were 
allowed  to  collect.  From  the  group  averages,  Nos.  268,  465,  471,  and 
931,  it  is  seen  that  the  bacterial  content  of  the  air  in  the  barn  was  low, 
even  though  the  cows  were  in  if  they  were  quiet  and  no  hay  or  bedding 
had  been  moved  for  some  time.  Immediately  after  bedding  or  feeding 
roughage  the  number  of  bacteria  in  the  air  was  much  greater,  while  an 
hour  later  it  was  reduced  about  one-third.  There  were  occasional  excep- 
tions to  this,  as  in  the  three  groups  on  March  10,  when  all  door  and 
windows  were  open.  At  the  same  time  there  was  a  strong  breeze  blow- 
ing, rapidly  replacing  the  dusty  air  with  air  from  out  of  doors,  which 
was  nearly  sterile. 

To  show  the  effect  of  having  the  barn  quiet,  November  30  all  stock 
was  let  out,  windows  and  doors  closed,  and  the  barn  locked  for  three 
hours,  after  which  an  average  of  six  exposures  gave  only  one-half  a 
colony;  ten  minutes  later,  after  having  moved  about  in  the  barn,  an 
average  of  six  exposures  gave  but  five-sixths  of  a  colony.  This  shows 
that  when  the  air  in  the  barn  remains  perfectly  quiet  for  some  time,  it 
becomes  comparatively  sterile. 

Half  an  hour  after  letting  in  the  cows  and  feeding  and  sweeping,  one 
exposure,  where  dust  was  plainly  visible,  showed  412  colonies,  and 
eleven  exposures  made  at  different  places  in  the  barn  where  there  was 
no  dust  visible,  averaged  151  colonies.  These  results  show  the  number 
of  bacteria  that  are  in  the  air  as  a  result  of  feeding  and  sweeping  when 
the  air  was  nearly  sterile  before.  One  hour  later  nine  exposures  aver- 
aged 84  colonies,  showing  that  the  dust  and  bacteria  soon  settled  out  of 
the  air.  Ten  minutes  later,  sixteen  cows  brushed  in  meantime  by  two 
men,  an  average  of  two  exposures  gave  858  colonies,  showing  that 
brushing  the  cows  had  increased  the  bacterial  content  of  the  air  over  ten 
times. 

Even  though  the  number  of  bacteria  caught  when  the  cows  were 
eating  hay  was  large,  the  increase  caused  by  brushing  the  cows  varied 
from  a  small  amount  in  one  case  to  over  ten  times  the  number  in  another 
case,  the  only  exception  being  when  there  was  a  strong  breeze  blowing 
through  the  barn,  for  in  such  cases  the  results  are  especially  uncertain. 

From  the  table  it  is  seen  that  the  number  of  bacteria  in  the  air  is 
greatly  increased  by  brushing  the  cows,  and  it  may  also  be  noticed  that 
the  bacteria  rapidly  settled  by  allowing  everything  to  remain  quiet  for 
from  ten  to  twenty  minutes. 

From  the  latter  half  of  Table  3,  beginning  with  exposure  No.  322,  it 
is  seen  that  dust  arising  from  different  sources  in  dairy  barns  may  be 
similar  in  amount  and  yet  differ  greatly  in  bacterial  content.  The 
average  of  four  exposures  made  where  dust  from  each  of  the  following 
sources  was  plainly  visible,  contained  colonies  as  follows:  corn  meal,  57; 
hay,  323;  bran,  418,  and  from  brushing  cows,  764.  It  is  seen  from  this 


1903.] 


PREVENTING  CONTAMINATION  OF  MILK. 


235 


that  dust  which  comes  from  brushing  cows  contains  about  twice  as  many 
bacteria  as  that  from  either  hay  or  bran,  and  thirteen  times  as  many  as 
dust  from  corn  meal.  This  is  doubtless  due  to  the  fact  that  bacteria 
find  on  the  cow  a  good  place  to  develop,  as  both  warmth  and  nutriment 
are  present.  The  dust  from  hay  comes  from  the  external  and  exposed 
parts  of  plants,  and  since  bran  is  from  the  external  portion  of  the  wheat 
kernel  it  is  natural  that  the  dust  from  these  be  heavily  laden  with 
bacteria,  as  the  exposed  parts  of  all  plants  are  more  or  less  covered  with 
these  organisms  Since  the  great  bulk  of  corn  meal  comes  from  the 
inner  portion  of  the  kernel,  which  is  sterile,  it  is  not  strange  that  dust 
from  fresh  corn  meal  contains  but  few  bacteria  compared  with  that  from 
other  feeds.  The  two  exposures  in  dust  from  musty  corn  meal,  in  group 
No.  628,  averaged  284  colonies,  while  an  average  of  four  exposures  in 
fresh  corn  meal  gave  in  one  case  57  colonies,  and  in  another  4£  colonies, 
showing  that  dust  from  musty  corn  meal  contains  bacteria  in  much 
larger  numbers  than  dust  from  fresh  corn  meal,  as  bacteria  multiply 
greatly  during  the  process  of  fermentation. 

Exposures  made  a  few  minutes  after  a  dust  had  been  raised  showed 
in  each  case  that  much  had  settled  from  the  air,  and  that  where 
there  was  no  movement  to  keep  up  a  dust,  the  air  soon  became  compara- 
tively sterile. 

TABLE  4. — BACTERIAL  CONDITION  OP  EXPERIMENTAL  MILKING  ROOM,  UNIVERSITY 

OF  ILLINOIS. 


s 

H) 

S 

o 
G 
H 

•3 

el 

Q 

Place  and  condition  of  exposure. 

Exposures  aver- 
aged. 

Colonies  devel- 
oped. 

257 

1897 
June  25 

Floor  damp,  sides  dry,  window  open,  damp  out- 
doors          .        

4 

0 

261 

July  2 

Window  closed,  cloudy  and  damp  

7 

1? 

July  10 

Small  window  open  all  day,  slight  breeze       .... 

4 

6| 

295 

5  min.  after  No.  289,  sides  and  ceiling  sprinkled 
with  hose  in  meantime  

3 

11 

300 

« 

Cow  being  brushed  3  ft.  distant  

1 

6174 

301 

" 

After  cow  had  been  brushed  4  min.  and  removed; 
room  quiet  4  min  

?, 

147 

305 

" 

30  min.  after  No.  301,  room  quiet  and  closed  in 
meantime  

3 

5} 

429 

Nov.  13 

After  room  had  been  closed  6  hours  

6 

7| 

435 

10  min.  after  No.  429,  just  after  sprinkling  sides 
and  ceiling  with  hose  

6 

19 

441 

447 

a 

50  min.  after  No.  435,  room  closed  in  meantime.  . 
2  min.  after  No.  441,  cow  brought  in  and  brushed 
1  min  

6 

?, 

4J 

262 

449 

ii 

After  cow  had  been  brushed  4  min.  and  removed 
from  room  

4 

32 

453 

ii 

3  min.  after  cow  had  been  removed  

11 

455 

ii 

7  min.  after  No.  453  . 

6 

3 

461 

<> 

8  min.  after  No.  455  

0 

236 


BULLETIN  No.  91. 


[December, 


The  results  of  exposures,  shown  in  Table  4,  were  obtained  in  an 
experimental  milking  room  where  the  conditions  were  more  completely 
under  control  than  in  the  barn ;  the  purpose  being  to  determine  the  con- 
dition of  the  air  in  a  room  that  had  been  vacant  for  some  time,  also  after 
sprinkling  the  sides  and  ceiling  with  a  hose,  immediately  after  brushing 
a  cow,  and  at  frequent  intervals  thereafter. 

From  this  table  it  is  seen  that  June  25,  when  the  floor  of  the  milking 
room  and  the  outside  air  were  damp,  four  exposures  were  sterile,  and 
July  2  seven  exposures  averaged  If  colonies. 

A  series  of  exposures  was  made  under  varying  conditions  July  10 
and  November  13,  and  from  these  it  is  seen  that  somewhat  fewer 
colonies  developed  upon  entering  a  room  than  after  thoroughly  sprink- 
ling the  sides  and  ceiling  with  a  hose,  as  the  force  of  the  water  seemed  to 
raise  a  slight  dust.  This,  however,  settled  rapidly,  for  as  soon  as  the 
dust  touched  any  wet  surface  it  adhered  to  it.  July  10  a  cow  was 
brought  into  the  nearly  sterile  air  of  the  room,  brushed  four  minutes, 
and  removed,  when  exposure  No.  300  was  made  and  6,174  colonies 
developed.  An  average  of  two  exposures,  group  No.  447,  made  after  a 
cow  had  been  brushed  one  minute,  gave  262  colonies,  showing  again 
that  the  dust  which  comes  from  cows  is  heavily  laden  with  bacteria.  It 
is  noticed  in  both  of  these  cases  that  the  dust  rapidly  settled  when  the 
room  remained  closed  so  that  there  were  no  currents  of  air,  and  in  the 
course  of  half  an  hour  the  air  was  practically  free  from  bacteria. 

TABLE  5. — BACTERIAL  CONDITION  OF  AIR  IN  DAIRY  ROOMS,  UNIVERSITY  OP  ILLINOIS. 


a  . 

e 

i 

Colonies 

•It 

3 

o 

1 

developed. 

i| 

a 

i 

Place  and  condition  of  exposure. 

U 

H 

<4H 

O 

§  rt 

•t>  j 

.2  g 

o£ 

o 

2. 

8  ° 

-u  O 

r 

di 

R 

i 

fcg 

JP 

1897 

10 

Jan.  13 

On  table  •  

2 

15 

11 

On  table  

2 

i 

12 

« 

On  table,  milk  cooling  

2 

0 

175 

April  24 

On  table,  room  closed  for  30  min  

2 

0 

327 

Sept.  14 

On  table,  milk  cooling  

3 

1 

330 

On  table  

1 

14 

1899 

621 

May  1  1    • 

On  table,  room  empty  

24 

A 

625 

On  table,  room  empty  

18 

708 

May  16 

On  table  when  bottling  milk  

5 

21 

913 

Sept.  16 

On  table  when  bottling  milk  

4 

Table  5  shows  the  average  number  of  colonies  developed  from  expo- 
sures made  in  dairy  rooms  which  have  cement  floors  and  painted  sides 
and  ceilings.  From  the  three  exposures  made  in  the  front  room,  which 
is  used  both  as  an  office  and  separating  room,  the  average  number  of 
colonies  developed  was  15.  In  the  bottling  room  everything  is  kept 


1903.] 


PREVENTING  CONTAMINATION  OF  MILK. 


237 


TABLE  6. — COLONIES  DEVELOPED  FROM  EXPOSURES  UNDER  UDDERS  IN  VARIOUS 

CONDITIONS. 


Laboratory  number  of 
group. 

Date  of  exposure. 

Number  of  exposures 
averaged. 

Average  number 
of  colonies  de- 
veloped; 
different  udders. 

Average  number  of  colonies  devel- 
oped; same  udder  before  and 
after  treatment. 

1 

o 
u 

•o 
'2 

<D 
ja 

"£ 
£ 

$ 

03 

Unwashed. 

Washed. 

Before  wash- 
ing. 

After  wash- 
ing. 

Before  wip- 
ing. 

a 

'Sti 

bJ 

01 

*S 

«4H 

< 

198 
313 
319 
331 
526 
534 

538 
554 
566 
568 
574 
580 
586 
592 
651 
656 
671 
676 
686 
690 
700 
746 
751 
761 
766 
776 
781 
791 
793 
799 
811 
817 
830 
835 
850 
855 
870 
920 
923 
927 

943 

947 
955 
958 
964 
967 
973 
976 
996 

1897 
May  4 
Sept.  14 

Oct.  20 

Dec.  8 
u 

1899 
April  13 

May  11 

May  16 

« 

« 
May  23 

May  28 

June  3 

u 

Sept.  16 

1901 

June  5 
u 

u 
u 

June  14 

u 

June  22 

3 
3 
3 
3 

8 
4 

16 
11 
2 
6 
6 
6 
6 
4 
5 
4 
4 
10 
3 
8 
8 
5 
10 
5 
10 
4 
9 
2 
4 
10 
5 
9 
2 
15 
5 
15 
15 
3 
4 
4 

4 
8 
3 
6 
2 
2 
2 
4 
5 

1631 

486 
219 

200 

2973 

90 

470 

133 

60 

421 

226 

211 

88 

8* 

230 

25 

157 

72 

372 

152 

8| 

25 

48 

90 

11 

127 

58 

6 

144 

286 

116 

269 

4 

33 

3 

56 

20 
27 
23 

19 

2301 

503 

1756 

512 

1614 

291 

1026 

369 

1586 

238 


BULLETIN  No.  91. 


[December, 


TABLE  6. — COLONIES    DEVELOPED  FROM  EXPOSURES  UNDER  UDDERS  IN  VARIOUS 
CONDITIONS. — Continued. 


Laboratory  number  of 
group. 

Date  of  exposure. 

Number  of  exposures 
averaged. 

Average  number 
of  colonies  de- 
veloped ; 
different  udders. 

Average  number  of  colonies  devel- 
oped; same  udder  before  and 
after  treatment. 

P 

0 
« 

•a 
| 

1 

A 

a> 
* 
X 
OB 

Unwashed. 

Washed. 

Before  wash- 
ing. 

£  t* 
fe-s 

5 

Before  wip- 
ing. 

a 

!i 

* 

1001 
1011 
1016 
1021 
1031 
1036 
1046 
1051 
1061 
1066 
1095  . 
1100 
1110 
1115 
1125 
1130 
1140 
1145 
1155 
1160 
1170 
1175 
Numbe 
avers 

Averae 

June  22 
June  24 

« 

a 

u 

June  27 

« 

u 

June  28 

H 
U 

r  of  exposur 
Lffed 

10 
4 
5 
10 
4 
10 
5 
10 
5 
8 
5 
9 
4 
9 
3 
8 
5 
10 
4 
9 
5 
10 
es 

346 

1401 

482 

iis 

i23 
i33 

229 
'421 
'262 

120 

202 

94 

266 

114 

448 

193 

'igi 

'313 
'407 

329 

849 

314 

26 

42 

74 

103 

58 

117 

27 

e  . 

362 

83 

615 

148 

630 

270 

12 

scrupulously  clean,  and  the  floor  is  usually  damp,  thus  keeping  the 
greater  part  of  the  dust  out  of  the  air.  Sixty  exposures  were  made  in  this 
room  at  different  times  of  the  year,  and  the  average  for  the  total  number 
was  one-third  of  a  colony.  More  than  half  of  all  colonies  developed  from 
the  bottling  room  were  from  five  exposures  made  when  bottling  milk; 
forty-seven  of  the  sixty  exposures  in  this  room  were  sterile.  In  other 
words,  a  dish  would  have  to  be  exposed  an  average  of  one  and  a  half 
minutes  to  catch  one  bacterium.  In  an  atmosphere  as  nearly  sterile  as 
this,  milk  becomes  contaminated  very  slowly,  even  where  a  large  surface 
is  exposed,  as  in  passing  over  a  cooler. 

To  learn  something  of  the  amount  of  contamination  that  takes  place 
during  milking,  and  how  much  this  may  be  reduced  by  washing  the 
udders,  420  petri  dishes  were  exposed  under  washed  and  unwashed 
udders.  The  average  number  of  colonies  developed  from  exposures 
made  under  washed  udders  was  192  and  under  unwashed  udders  578, 
or  three  times  as  many.  The  group  averages  from  these  exposures  are 
shown  in  Table  6. 


1903.1 


PREVENTING  CONTAMINATION  OF  MILK. 


239 


As  a  rule,  washing  udders  makes  a  marked  reduction  in  the  number 
of  colonies  developed  from  exposures  made  under  them.  This  difference 
is  much  greater  in  some  cases  than  in  others.  The  most  noticeable 


CUT  5. — IN  MID-WINTER. 


PROPERLY  CLEANED.'TO,  PREVENT  ALL/ POSSIBLE 
•  CONTAMINATION      " 


difference  was  obtained  December  8,  when  an  average  of  eight  •  expo- 
sures, No.  526,  showed  2,973  colonies  before  washing,  while  an  average 
of  four  exposures  made  under  the  same  udder  after  washing  showed  only 
90  colonies.  In  other  words,  the  contamination  which  took  place'in  this 
instance  was  thirty-three  times  greater  before  washing  than  after. 

In  a  few  cases  a  less  number  of  colonies  developed  from  exposures 
made  under  unwashed  udders  than  from  those  made  under  the  same 
udders^after  washing.  A  possible  explanation"  for  this  is  that  dirt  from 


240 


BULLETIN  No.  91. 


[December, 


the  unwashed  udders  fell  in  larger  particles,  and  thus  the  dishes  were 
contaminated  in  fewer  places,  although  a  greater  total  contamination 
took  place,  for  a  colony  developed  on  a  petri  dish  may  have  originated 


CUT  6. — AFTER  A  RUN  OF  THREE  WEEKS  ON  PASTURE.     IMAGINE  THE  SOURCE  OF 
CONTAMINATION  DURING   WINTER. 

from  a  single  bacterium  or  from  a  particle  of  dirt  large  enough  to  be  seen 
with  the  naked  eye  and  containing  thousands  of  bacteria. 

It  should  be  borne  in  mind  that  the  udders  used  in  this  experiment 
were  not  only  apparently  clean,  but  they  had  been  washed  regularly  each 
day  before  milking,  and  in  all  probability  there  was  much  less  dirt 
adhering  to  them  than  to  udders  that  had  never  been  washed.  With 
soiled  or  muddy  udders,  such  as  are  frequently  found  in  dairies,  the 
benefits  derived  from  washing  are  much  greater  than  these  results  show. 


1903.] 


PREVENTING  CONTAMINATION  OF  MILK. 


241 


IM  CO  (M  1-1  <N  <N 


i 


be 

OO^F>OGOOi-HT-<i— ilOcOOCOCOi— irHT^-^tioOOOOOOOi— i  i— I  i— i  i— I        ?3 
--l(N(M(NeOCOCO?OlN(N(N  <M(N<N<N'-H.-ii-H,-i<M(N<N<N        ft 


OOOOi-iOt-iOOOO^HT—  (i—  ii—  ii—  lOi—  i(N<Nr-(rH(NCO' 


1-1          03 

...S-4 


HD  t>«  t»  CJ  W  O  00 


•<  i 


i  (M  (N  IM(M  iM        <N 


242 


BULLETIN  No.  91. 


[December, 


o£ 

I 

«  3 

o  w 
M  £ 

s« 

H 

w   . 
2  v 

SB 

«i 
§^ 

^^ 

i 

w 
PQ 


O 


1903.]  PREVENTING  CONTAMINATION  OF  MILK.  243 

WEIGHT  OF  DIRT  WHICH  FALLS  INTO  MILK  DURING  MILKING. 

The  results  shown  in  Table  7  were  obtained  for  the  purpose  of  deter- 
mining by  weight  the  amount  of  filth  which  falls  into  milk  during  the 
process  of  milking,  and  how  much  this  may  be  reduced  by  washing  the 
udders. 

After  several  trials  with  three  different  milkers  on  thirty  cows,  it  was 
found  that  it  required  an  average  of  4£  minutes  to  milk  a  cow.  A  glazed 
dish,  eleven  inches  in  diameter,  the  size  of  an  ordinary  milk  pail,  was 
held  under  a  cow's  udder  4£  minutes,  while  the  milker  went  through 
motions  similar  to  those  made  in  milking,  but  not  drawing  any  milk. 
The  amount  of  dirt  which  fell  into  the  dish  during  the  operation  was,  of 
course,  approximately  the  same  as  would  have  fallen  into  the  milk  during 
the  milking  process.  The  dirt  caught  in  the  dish  was  then  brushed  into 
a  small  glass  weighing  tube,  such  as  shown  in  cut  9,  the  udder  washed, 
and  the  process  repeated.  Both  tubes  were  then  placed  in  a  desiccator, 
and  after  drying  twenty-four  hours  to  remove  moisture,  were  accurately 
weighed  in  a  chemical  balance. 

It  will  be  noticed  that  the  weight  of  dirt  which  fell  from  udders 
varied  greatly  when  there  appeared  to  be  the  same  amount  on  them. 
The  reason  for  this  is  that  the  amount  of  dirt  which  falls  from  a  clean,  a 
soiled,  or  a  muddy  udder  depends  upon  the  character  of  the  dirt,  the 
amount  of  hair  on  the  udder,  its  shape,  the  length  of  the  teats,  etc. 

Seventy-five  trials  were  made  at  different  seasons  of  the  year  with 
three  classes  of  udders,  those  apparently  clean,  soiled,  and  muddy. 
With  udders  that  were  apparently  clean,  it  was  found  that  an  average  of 
3£  times  as  much  dirt  fell  from  the  unwashed  udders  as  from  the  same 
udders  after  they  were  washed.  With  soiled  udders  the  average  was  18, 
and  with  muddy  udders  90  times  as  much  dirt  from  the  unwashed  as 
from  the  washed. 

The  average  weight  of  dirt  falling  from  muddy  udders  during  the 
time  of  milking  was  found  to  be  .8831  of  a  gram.  Since  in  one  ounce 
there  are  28£  grams,  an  ounce  of  dirt  would  fall  into  the  milk  for  every 
32  milkings.  From  a  year's  records,  kept  by  the  department  of  dairy 
husbandry,  of  eight  herds  containing  144  cows,  it  was  found  that  one 
gallon,  or  8f  pounds,  was  the  average  yield  at  a  milking.  On  this  basis, 
in  32  milkings,  275  pounds  of  milk  would  be  produced  containing  one 
ounce  of  filth.  With  the  same  udders  after  they  were  washed,  24,030 
pounds  of  milk,  or  90  times  as  much,  could  be  obtained  before  the] 
amount  of  filth  it  contained  would  reach  one  ounce.  This  shows  the 
decided  advantage,  in  the  production  of  clean  milk,  of  washing  the 
udders  before  milking. 


244 


BULLETIN  No.  91. 


[December, 


CUT  9. — PETRI  DISH,  SHOWING  COLONIES  DEVELOPED  FROM  EXPOSURE  DURING 
MILKING  IN  WELL-KEPT  DAIRY  BARN. 


TABLE  8. — AVERAGE  NUMBER  OF  COLONIES  DEVELOPED  FROM  EXPOSURES  MADE  IN 

DIFFERENT  PLACES  AND  TIME  MILK  WOULD  HAVE  TO  STAND  AT  THOSE 

PLACES  TO  RECEIVE  AS  MUCH  CONTAMINATION  FROM  THE 

AlR  AS  IT  WOULD  UNDER  AN  UNWASHED  UDDER 

DURING   THE   4£   MlNUTES   OF   MlLKING. 


Ave.  number  min. 

Num- 

Average 

milk  would  have  to 
stand  at  the  different 

Place  of  exposure. 

expo- 
sures 
aver- 
aged. 

colonies  de- 
veloped 
from  Vz  min. 
exposure. 

places  to  receive  as 
much  contamination 
from  the  air  as  it 
would  under  an  un- 
washed udder  during 

Time  in 
days. 

the  4  J-  min.  of  milking. 

Open  field  

43 

A 

2890 

2 

Barnyard  .•  .  . 

51 

13 

200 

Well  kept  barn  during  milking  .  . 
University  barn  during  milking  . 

10 
46 

32 

38 

81 
68 

'•'•\ 

Poorly  kept  barn  during  milking 

21 

168 

15 

Barn  empty,  closed  3  hours  .... 

12 

§ 

3901 

2$ 

Before  feeding  

9 

46 

57 

After  feeding    

34 

109 

24 

After  brushing  cows  

38 

307 

8 

Under  apparently  clean  unwash- 

ed udder  

158 

578 

4A 

Under  washed  udder  

262 

192 

14 

Bottling  room  

60 

i 

7803 

55 

Dairy  front  room.  . 

3 

15 

173 

1903.] 


PREVENTING 'CONTAMINATION  OF  MILK. 


245 


CUT  10. — PETRI  DISH,  SHOWING  COLONIES  DEVELOPED  FROM  EXPOSURE  DURING 
MILKIXG  IN  POORLY  KEPT  DAIRY  BARN. 

CONCLUSIONS. 

The  results  of  the  work  described  in  this  bulletin  are  of  vital  impor- 
tance to  the  practical  dairyman,  as  they  show  that  extreme  cleanliness 
is  absolutely  essential  to  the  most  successful  dairying. 

Table  8,  which  contains  averages  of  all  exposures  made  in  different 
places,  shows  where  and  under  what  conditions  milk  becomes  contami- 
nated most  rapidly,  and  that  the  bacterial  content  of  milk  may  be 
greatly  reduced  by  a  few  simple  precautions  easily  carried  out  in  any 
dairy.  The  nearer  the  ideal  condition  is  reached,  the  fewer  bacteria  in 
the  milk,  and  the  more  wholesome  will  be  not  only  the  milk  itself,  but 
the  products  made  from  it, 'and  the  better  their  keeping  quality. 

From  exposures  made  out  of  doors  it  was  found  that  air  in  the  open 
field  was  nearly  sterile,  since  an  average  of  less  than  one  colony  devel- 
oped for  each  half-minute  exposure,  while  in  the  barnyard  an  average 
of  13  colonies  developed  in  the  same  time.  This  increase  over  the  num- 
ber in  the  field  was  doubtless  due  to  the  fact  that  the  ground  in  the 
barnyard  was  bare  and  dry,  and  the  cows  moving  about  created  a  dust. 

In  a  well-kept  dairy  barn,  where  the  floor  was  swept  clean  and  no 


246 


BULLETIN  No.  91. 


[December, 


cobwebs  were  allowed  to  collect,  32  colonies  developed  from  exposures 
made  when  milking  was  in  progress,  and  in  a  poorly  kept  barn,  where 
there  was  much  dust  on  the  floor  and  cobwebs  were  numerous,  168  colo- 
nies developed,  or  five  times  as  many.  This  shows  the  decided  advan- 
tage of  keeping  the  dairy  barn  as  clean  as  possible. 

To  show  the  effect  of  having  everything  in  the  milking  stable  quiet 
for  some  time,  the  University  dairy  barn  was  swept,  after  the  cows  were 


CUT  11. — PETRI  DISH,  SHOWING  COLONIES  DEVELOPED  FROM  EXPOSURE 
UNDER  APPARENTLY  CLEAN  UNWASHED  UDDER. 

let  out,  and  closed  for  three  hours;  exposures  then  made  showed  an 
average  of  less  than  one  colony. 

When  the  cows  were  in,  but  before  feeding,  46  colonies  developed  for 
each  half-minute  exposure;  immediately  after  feeding  roughage  109 
colonies  developed,  and  after  brushing  the  cows  the  number  was 
increased  to  307.  These  results  indicate  that  feeding  roughage  and 
brushing  cows  greatly  increase  the  bacterial  content  of  the  air.  Such 
operations,  therefore,  should  not  take  place  immediately  before  milking, 
but  some  time  should  intervene  to  allow  the  dust  to  settle. 

By  far  the  greatest  source  of  contamination  in  milk  is  the  cow  her- 
self, and  the  greater  part  of  this  contamination  comes  from  the  udder, 
unless  that  is  washed  before  milking.  The  one  hundred  fifty-eight 


1903.]  PREVENTING  CONTAMINATION  OP  MILK.  247 

exposures  made  under  unwashed  udders  averaged  578  colonies,  or  three 
times  as  many  as  the  average  number  developed  from  exposures  made 
under  the  same  udders  after  washing.  Table  7,  giving  the  weight  of  dirt 
caught  under  udders  in  different  conditions,  shows  that  three  and  one- 
half  times  as  much  dirt  fell  from  apparently  clean  unwashed  udders  as 
from  the  same  udders  after  washing.  Thus  it  is  seen  that  in  the  case  of 
apparently  clean  udders  the  ratio  of  the  weight  of  dirt  caught  corre- 


CUT  12. — PETRI  DISH,  SHOWING  COLONIES  DEVELOPED  FROM  EXPOSURE 
UNDER  WASHED  UDDER. 

sponds  very  closely  with  the  ratio  of  the  number  of  colonies  developed 
from  exposures  under  washed  and  unwashed  udders.  The  amount  of 
contamination  from  soiled  or  muddy  udders  was  not  determined  from  a 
bacteriological  standpoint;  the  benefit  derived  from  washing  such  udders 
was  determined  only  by  the  comparative  weights  of  dirt  caught  under 
them.  With  soiled  udders  the  weight  of  dirt  was  eighteen  times  greater 
from  the  unwashed  udders  than  from  the  same  udders  after  washing,  and 
with  muddy  udders  it  was  ninety  times  greater. 

In  the  University  of  Illinois  dairy  rooms,  which  have  cement  floors 
and  painted  sides  and  ceilings,  there  are  comparatively  few  bacteria  in 
the  air.  This  is  especially  true  of  the  milk  bottling  room,  where  the  floor 


248  BULLETIN  No.  91.  [December, 

is  frequently  scrubbed,  and  is  usually  damp,  as  an  average  of  sixty  expo- 
sures showed  only  one-third  of  a  colony. 

From  the  averages  in  the  preceding  table  it  is  seen  that  the  amount 
of  contamination  that  milk  receives  from  the  bacteria  of  the  air  falling 
into  it,  depends  entirely  upon  the  conditions  under  which  it  was 
exposed.  The  table  also  shows  the  length  of  time  it  would  take  milk 
exposed  in  the  pail  to  receive  the  same  amount  of  contamination  at  the 
designated  places  that  it  gets  from  an  unwashed  udder  during  milking, 


CUT  13. — PETRI  DISH,  SHOWING  COLONY  DEVELOPED  FROM  EXPOSURE  IN 
MILK  BOTTLING  ROOM. 

which  time  was  found  to  be  4£  minutes.  Since  an  average  of  578  colo- 
nies developed  on  sixty-three  square  centimeters  of  surface  for  every 
half-minute  exposure  under  an  unwashed  udder,  in  4^  minutes  the 
number  would  have  increased  to  5,202.  In  the  milk  bottling  room  an 
average  of  one-third  of  a  colony  developed  on  a  like  area  for  every  half- 
minute  exposure,  or  two- thirds  per  minute.  A  pail  of  milk  would,  there- 
fore, have  to  stand  exposed  to  the  air  in  this  room  7,803  minutes,  or 
more  than  five  days,  to  receive  as  much  contamination  as  it  would 
under  an  apparently  clean  unwashed  udder  during  milking.  This 
emphasizes  not  only  the  great  importance  of  washing  the  udders  before 


1903.]  PREVENTING  CONTAMINATION  OF  MILK.  249 

milking,  but  also  of  having  the  dairy  rooms  and  all  surroundings  as  clean 
and  the  air  as  free  from  dust  as  possible  wherever  dairy  products  are 
handled. 

An  effort  was  made  to  determine  the  different  species  of  bacteria  that 
gain  access  to  milk,  but  in  the  present  state  of  development  of  the  science 
of  bacteriology,  this  is  difficult  to  do  satisfactorily.  For  the  practical 
dairyman  it  is  sufficient  to  say  that  a  majority  of  the  forms  found  grow 
readily  in  milk.  Many  of  the  species  produce  visible  changes  in  milk, 
such  as  curdling  or  peptonizing,  while  others  affect  the  flavor. 

It  should  be  borne  in  mind  that  a  great  majority  of  the  species  of 
bacteria  that  gain  access  to  milk  do  not  possess  the  power  to  produce 
disease,  and  are  not  injurious  to  healthy  adults,  although  many  of  them 
are  likely  to  produce  disorders  of  digestion  in  infants  and  invalids. 

Paying  special  attention  to  cleanliness  in  every  step  of  the  production 
and  care  of  milk  will  result  not  only  in  clean  milk,  but  in  a  marked 
reduction  in  the  number  of  bacteria  it  contains,  which  will  greatly 
lengthen  its  keeping  qualities.  That  the  desired  results  may  be 
obtained,  care  must  be  constantly  exercised.  It  is  of  little  consequence 
to  practice  extreme  cleanliness  in  all  of  the  steps  of  milk  production  but 
one,  and  be  filthy  about  that  one,  as  this  spoils  the  whole.  Even  if  the 
majority  of  species  of  bacteria  which  ordinarily  gain  access  to  milk  are 
not  dangerous  to  health,  no  one  cares  to  consume  milk  in  which  a  sedi- 
ment is  found  at  the  bottom  if  it  is  allowed  to  stand  for  a  short  time. 
Frequently  much  filth  is  allowed  to  get  into  milk  during  milking,  and 
many  milkers  practice  the  filthy  habit  of  keeping  the  teats  wet  with  milk 
during  the  milking  process,  yet  after  it  is  drawn  the  greatest  care  is 
exercised  that  no  dust  or  dirt  gain  access  to  it.  As  far  as  the  final  result 
is  concerned,  all  painstaking  care  in  the  subsequent  operations  is  lost 
because  of  the  careless  work  at  the  beginning  during  the  process  of 
milking,  for  if  filth  once  gains  access  to  milk,  no  amount  of  care  after- 
wards can  remedy  the  difficulty.  It  is,  therefore,  of  the  greatest  impor- 
tance to  the  advancement  of  better  dairying  that  special  emphasis  be 
placed  upon  the  operation  where  milk  is  liable  to  receive  the  most  con- 
tamination. The  work  reported  in  the  preceding  pages  shows  that  the 
greatest  source  of  contamination  in  milk,  as  ordinarily  produced,  is  the 
cow  herself,  and  this  is  doubly  important  because  it  is  the  source  which 
is  given  the  least  attention  in  actual  practice. 


UNIVERSITY  OF  ILLINOIS-URBANA 


